We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si1−xGex heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor ν=3 (Δ3) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of Δ3 on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of Δ3 before and after the coincidence.
@article{arxiv.cond-mat/0601637,
title = {Valley splitting of Si/SiGe heterostructures in tilted magnetic fields},
author = {K. Lai and T. M. Lu and W. Pan and D. C. Tsui and S. Lyon and J. Liu and Y. H. Xie and M. Muhlberger and F. Schaffler},
journal= {arXiv preprint arXiv:cond-mat/0601637},
year = {2007}
}